The present invention is directed to a measuring while drilling tool. Various and sundry measuring while drilling tools have been fabricated in the past. The present invention offers improved performance over them. First of all, this tool does not require internal electrical circuitry, batteries and the like. In some wells, the bottom hole temperature is so high that electrical components are seriously derated and do not perform very well. The present invention is able to perform quite well at elevated temperatures because it is devoid of batteries and electronic components.
The present invention is particularly able to form an indication of the angle of inclination of the tool. In addition to that, it forms an output signal indicative of the heading relative to magnetic north. Other outputs are incorporated. One of the best and most desired sensors is a mechanism indicating the inclination of the tool. This is particularly useful in determining whether or not the tool is oriented vertically or at some other angle departing from the vertical. In the drilling of oil wells, it is often necessary to control their drift or direction. Sometimes, they are intentionally deviated from the vertical. In any case, this must be indicated at the surface to control deviation. Techniques exist whereby angular drift or deviation from the vertical can be measured.
Other sensors can be used. In any event, without regard to the specific nature of the sensors, it is very helpful to further incorporate devices which form two calibration pulses. The calibration pulses serve as references or standards against which the variables can be calibrated. Two are especially helpful. This is helpful to calibrate the output which is read in the mud pressure line connected to the drill string. The attenuation varies as the well drills deeper and deeper. As it drills deeper, it is necessary to compare the calibration signals available. The mud column viscosity encountered as the well becomes deeper may change and thereby vary the signals sensed at the surface, but, as long as the calibration output signals are available, they serve as a comparative standard, and correct data can be read at the surface.